The proposed research is a case-control epidemiologic study of risk factors for colon adenomas. Colon adenomas are neoplastic growths which are presumed precursors of colorectal cancer. The epidemiologic features of adenomas have received little study. Identification of risk factors for colon adenomas will improve our understanding of colorectal cancer etiology and provide a rational basis for future intervention studies to prevent colon adenomas and colon cancer. The specific aim of the study is to determine whether risk factors for colon cancer are also risk factors for adenomas. The study will evaluate the role of diet and other factors such as obesity, use of estrogens, parity, exercise, sedentary occupation, bowel habits, and cigarette smoking in adenoma etiology. Exploratory analyses will assess the relationship, if any, between these risk factors and degree of cellular atypia, polyp type, and polyp size, and whether these risk factors help predict adenoma recurrence. Cases will be patients with one or more pathologically confirmed adenomas found at colonoscopy. Controls will be colonoscopy patients found to be adenoma-free. Subjects who meet eligibility requirements will be weighed, measured and interviewed in-person following colonoscopic examination. Interviews will focus on diet using a quantitative food frequency questionnaire, lifestyle factors, and medical history. Three hundred cases and 300 controls are expected to be recruited and studied over a three- year period. Standard methods for analysis of case-control data will be employed.